The breast is found as a paired organ on the anterior chest wall, anterior to the pectoralis muscle and the serratus anterior muscle.
This coronally reformatted image of the anterior aspect of the chest of a 24 year old female shows the breasts resting on the anterior chest wall, anterior to the barely visible pectoralis muscles. Courtesy Ashley Davidoff MD TheCommonVein.net 42682
The breast overlies the second to sixth or seventh rib, lying within the hypodermis and superficial to the anterior fascia of the pectoralis major muscle.
Landmarks of its medial and lateral borders correspond to the lateral sternal border and laterally to the anterior axillary fold.
The breasts develop along the lateral-line, primitive milk streak or “galactic band”. As previously noted this line runs from the axilla through the nipples arcing slightly anteriorly and then coursing back to the inguinal regions.
In the human, the breasts seem to have been positioned under the watchful eye of the nursing mother whereas in animals it seems like they have been positioned for protection from injury. In the cow, elephant, horse, goat and deer they are in the inguinal region and in the whale the breasts are on either side of the anus. The monkey and bat have breasts that are positioned anteriorly and laterally – similar to positioning in the human.
The glandular tissue as stated above is radially oriented around the nipple with a preponderance of parenchyma in the upper outer quadrant in the tail of Spence.
The glandular tissue is normally separated from the pectoralis muscles of the anterior chest wall by a fat plane and from the skin by adipose tissue as seen in the next image. This is called the retromammary layer of fat.
A cross section through the female chest at the level of the nipples reveals an inverted v-shaped tissue, or triangular shaped structure (pink) which represents the mammary apparatus – a combination of glandular tissue, ducts, intralobar fat and stroma.. Note that the glandular tissue has fat both anteriorly and posteriorly to it. The detail of these layers is expanded in the “parts” section. Courtesy Ashley Davidoff MD TheCommonVein.net 43926b05b
Note in this case of inflammatory carcinoma of the right breast, the fat plane between the glandular tissue and the anterior chest muscle has been lost as the process has invaded that space. Courtesy Ashley Davidoff MD TheCommonVein.net 20042
Applied Anatomy
In a patient with breast carcinoma the involvement of the skin or chest wall upstages a localized breast mass to stage IIIB which has important therapeutic implications.
Character
The adipose tissue in general makes up 80-85 % of the breast gives it a soft feel and together with the stroma and glands the breast is characterized as having a rubbery feel. However, in general, the glandular portion of the breast has a firm, slightly nodular feel, while the fat is almost always soft.
As we have noted above there are breasts where 80% of the breast is fibro-glandular and others where the fat predominates. It is more common to see the dominance of fat in the breast of older patients, and fibro-glandular dominance is usually seen in the young, though there is wide variation.
The breasts become firmer in pregnancy and lactation, but become softer and less rubbery with aging, mostly due to glandular regression and proliferation of fat.
Consistency of breast lobes varies from woman to woman, and will vary during the cycle, and may even vary in an individual from one side to the other.
The ducts of the breast are usually not palpable unless they are engorged with milk, inflamed or contain a tumor.
The areola is of a delicate rose colored hue in the nulliparous patient but enlarges and darkens with pregnancy, and may even become black. After pregnancy it may lighten but it never returns to its former rose colored hue. The nipple also starts out as rose-colored structure, usually being slightly darker than the areola and darker than the skin. It also darkens with pregnancy.
Applied Anatomy
The discrepancy in textures between the adipose tissue and the mammary apparatus, allows one to outline the lobes by carefully palpating the breast. When the breasts feel thick and lumpy the entity of fibrocystic change probably exists. This finding implies that the fibro-glandular elements are enlarged. This enlargement is not necessarily abnormal.
The finding of a mass or a focally enlarged and hardened part of the breast is a significant finding and further characterization is important. It is essential to determine the mobility of the mass and get a feel as to whether it is tender (usually a finding in benign disease) whether it is fixed to the skin or deep muscles (a bad sign) and whether there are associated findings such as other masses, nipple discharge, or regional axillary adenopathy.
The radiographic difference in density between the parenchymal tissue and the fat allows structural evaluation and forms the basis for mammographic imaging, US imaging CT scanning and MRI.
This normal CT scan of a 24year old female shows the difference between the soft tissue density of the glandular and stromal tissue on the one hand (gray structures of the breast) and the adipose tissue of the breast on the other (charcoal black) Courtesy Ashley Davidoff MD TheCommonVein.net 42675
The intrinsic differences in the proton density of the mammary apparatus and adipose tissue enable distinction on the MRI scan. In the image above the fat of the breast is relatively dark due to fat suppression techniques, and the mammary apparatus is gray. Within the mammary apparatus the distinction between stromal tissue and glandular tissue cannot be made. Courtesy Priscilla Slanetz MPH TheCommonVein.net 42825b01
The strength of ultrasound technology in the breast is its ability to define the nature of palpable masses. In the first example above a palpable mass is clearly characterized as a cyst with its anechoic nature and through transmission, whereas the lesion below is clearly a complex and solid lesion. Ultrasound of the breast is used to answer specific focused questions – cystic or solid? Courtesy Priscilla Slanetz MD MPH TheCommonVein.net 42840c (combined 42883 42840)
Mammography is a high resolution technique that is best suited for identifying subtle masses, calcifications, and architectural distortions. The upper image reveals a dense breast meaning that the fibroglandular elements dominate while the breast in the lower image represents a fatty breast. 43868c (combination of 42868 42864) Courtesy Priscilla Slanetz MD MPH TheCommonVein.net
Diseases Carcinoma
Masses
An irregularly shaped mass, particularly if spiculated, is concerning for malignancy. A spiculated lesion is concerning whether it is identified on mammography, ultrasound, MRI or CT. The density of malignant lesions is also slightly greater than soft tissues. The high density of a carcinoma is characteristic of the scirrhous carcinoma.
This mammogram is blatantly positive for a dense, irregularly shaped mass that extends to, and involves the chest wall. Most cases are far more subtle than this case. The patient had an inflammatory breast carcinoma. Note that by convention mammographic images are projected with the left breast to your left and the right breast to your right – the opposite to the projections of cross sectional images. Courtesy Priscilla Slanetz MD MPH TheCommonVein.net 42747
This is an MRI of the right breast of a 78 year old patient with a remote history of invasive lobular carcinoma. The finding on the MRI is characterized by an enhancing spiculated mass. Recurrent carcinoma was present at pathology. Courtesy Priscilla Slanetz MD MPH TheCommonVein.net 42977
Calcifications
Calcifications that are associated with malignancy are usually small (<0.5 mm). A magnifying glass is an essential tool to evaluate the breast since the malignant calcifications may be too small to see with the naked eye. The calcifications are characterized by their pleomorphic shape, meaning that they have a heterogeneous nature. They may be fine and granular, and or linear, and or branching. Their distribution is also varied so that they could be clustered, regional, diffuse, or segmental.
Benign diseases
Benign breast masses are common and include predominantly fibroadenomas and fibrocystic disease. Cysts are part of the fibrocystic group of diseases.
Fibroadenomas are the most common breast lesion particularly in women under the age of 40. It is a benign neoplasm of the stromal and epithelial elements. The characteristic finding of a fibroadenoma is its smooth borders on mammography and US.
This mammogram of the left breast of a young adult female reveals a well circumscribed mass that proved to be a fibroadenoma. Courtesy Priscilla Slanetz MD MPH TheCommonVein.net 42913
This US of the left breast of a young adult female reveals a well circumscribed well circumscribed mass that proved to be a fibroadenoma. Courtesy Priscilla Slanetz MD MPH TheCommonVein.net 42914
Relations
The mammary apparatus itself is completely surrounded by adipose tissue with a superficial layer lying deep to the dermis and the retromammary layer lying anterior to the pectoralis major muscle. Outside of the breast proper, the most important structural relation of the breast is the pectoralis major muscle and its fascia which form the posterior border of the breast. The serratus anterior to lesser extent also forms a part of the posterior border. Its other borders include the clavicle superiorly, the sternum medially, 6th and 7th rib inferiorly.
Applied Anatomy
The involvement of the pectoralis fascia by a malignant mass is an important consideration in the staging of breast carcinoma which was discussed above. The pectoralis muscle can be identified by CTscan, MRI and also by ultrasound.
This ultrasound image shows the deep structures of the breast – most posteriorly is the pectoralis muscle, the pre-pectoral fascia, (thin white lines) retromammary fat which is relatively hypoechoic, the nodular appearance of the glandular tissue and the skin. Courtesy Ashley Davidoff MD TheCommonVein.net 43848